1. Field of the Invention
The present invention relates to a method of accessing an on-chip read only memory (ROM) and a computer system thereof, and more particularly, to a method of accessing an on-chip ROM and a computer system thereof, capable of increasing the operation speed of the computer system by combining addresses of the ROM and extending an output data width of the ROM.
2. Description of the Prior Art
In a computer system, memories can generally be classified into two types: external and on-chip. The external memories have larger storage space and need longer access time (e.g. usually hundreds of system clock cycles). The on-chip memories are high speed internal memories used for temporary storage of calculations, data, or other works in progress, where memory data are accessed in shorter time (e.g. usually within one system clock cycle). The on-chip memories are provided for the processor (e.g. central processing unit (CPU)) to perform fast retrieval, and can be further classified into random access memory (RAM) and read only memory (ROM). The on-chip RAM is usually used for storing temporary data or instruction codes, and the on-chip ROM stores data for system initializing or boot procedure. For some applications, a computer system may have only the ROM without any RAM.
With process advances, the frequency of the system clock becomes faster; hence timing requirements for accessing these on-chip memories become more critical to the computer system. Access speeds of the on-chip RAM and the on-chip ROM are different in nature. In general, in comparison with the on-chip RAM, the on-chip ROM has a lower access speed and a larger access time delay may be generated in the access path for the on-chip ROM, such that this access path may become a critical path in some systems or for some application. As a result, the clock frequency and operation speed of the computer system will be limited due to the access of the on-chip ROM. Thus, there is a need for improvement over the prior art.